G, Subtemporal exposure in another specimen. The PComA is larger than shown in D and E. The oculomotor nerve passes forward between the PCA and the superior cerebellar arteries. H, The exposure has been extended further posteriorly along the side of the brainstem to the quadrigeminal cistern. The tentorium has been divided to expose the upper part of the cerebellum. The PCA and superior cerebellar artery encircle the brainstem to reach the quadrigeminal cistern. The P2 is divided into a P2A that courses in the crural cistern between the uncus and cerebral peduncle, and a P2P that courses in the ambient cisterns between the parahippocampal gyrus on the midbrain. The P3 courses in the quadrigeminal cistern. The trochlear nerve arises below the inferior colliculus and crosses above the branches of the superior cerebellar artery. I, The exposure has been extended further posteriorly, above the tentorium to the left half of the quadrigeminal cistern. The tributaries of the vein of Galen have been retracted to expose the pineal. The PCA courses above the tentorium and the superior cerebellar artery below. The trochlear nerve arises below the inferior colliculus and passes around the brainstem. J, The exposure has been directed below the tentorium. The internal cerebral veins exit the roof of the third ventricle and the basal veins exit the basal cisterns to join and form the vein of Galen. The P3 courses through the quadrigeminal cistern. K, Midline infratentorial exposure. The pineal is exposed between the posterior cerebral arteries and basal veins and below the internal cerebral veins. The exposure into the fissure between the cerebellum and midbrain is not as great as can be achieved when the exposure is directed off to the side of the vermian apex in a paramedian location as shown in J. L, Enlarged view of the midline infratentorial exposure. (Images courtesy of AL Rhoton, Jr.)